Something very wrong with a cell

[StrapYourSelfIn]

I recently ran my headway 36v 10ah Headway battery back till it cut out. I thought it strange as I got substancially less milage out of it than usual.

(It is on a skateboard)

I charged it at workl and due to running around for meetings it the green light was on for about 1 hour with the charger still connected. I did notice however every now and then the charger would kick off and charge a bit. I took it for them charging.

I went to go home and the board would go, so took it back to the office and pulled it apart.
I could get it to run the motor for a few seconds and cut off.

Removed the BMA and same thing.

I came back with a multimeter and found all the cell were ballpark 3.37 - 3.38 except for one cell which reads 42.9 which is ballpark what the cells all fully charged register at.

How can this be as it doent make sense at all

 

[Tench]

Did you meen your board wouldn't go? and check the cell voltages you wrote down, guessing what is a typo and what isn't makes helping a little harder.

 

[StrapYourSelfIn]

The board runs with and without the bms attached for a few seconds.

no it isnt a typo
3.37 - 3.38 except for one cell which reads 42.9
thus the title

Something very wrong with a cell


it is a 12 cell 3.2 volts 10 Ah pack

 

[StrapYourSelfIn]

ad I meant what the full pack registers at not a single cell. The cell is the first on the negative end if that matters

(-) -|42.9|- -|3.38|-|3.38|-|3.38|-|3.38|-|3.38|-|3.38|-|3.38|-|3.38|-|3.38|-|3.38|-|3.38|-|3.38|-(+)

Thats what it looks like

 

[StrapYourSelfIn]

correction

(-) -|42.9|- -|3.38|-|3.38|-|3.38|-|3.38|-|3.38|-|3.38|-|3.38|-|3.38|-|3.38|-|3.38|-|3.38|-(+)

 

[Teh Stork]

You're measuring full pack voltage.

 

[Schlafmutze]

Cell at 42 volts you say?

 

[StrapYourSelfIn]

now its showing .31 volts.
i tested it out of the series and whilst in it and even when charging seperatley it cut off.

Going to take it back down stairs and see if it charges now

ALSO READ THE TITLE

"Something very wrong with a cell"

The volt charge keeps going all over the shop and I am using a cell thats constant as a check of the multi meter

For the record when i say 42v i stepped away before rationalising the cell cannot hold that

 

[StrapYourSelfIn]

ok dont understand but found how it displays that high, if i attempt to charge it the charger does not kick off but the volts climb to 42+. they stay there until I turn off the charger and they will reduce to .31 (circa)

 

[Tench]

What does that cell measure if you isolate it from the pack? and what voltage do you see on the wires with the cell removed from between them?

 

[StrapYourSelfIn]

When isolated and left alone it has .31 Volts

If i put it on the pack i shows exactly the addition of all cells and this .31

If I put it on charge it goes to 42.9 then when i switch it off it reduces to .31

I know the cell is shagged have already sent an email to get it replaced..

Main question is,could the BMS have played a part and do i need to maybe send that back. It was extremely hot as in smelt when I opened the case.

 

[StrapYourSelfIn]

sorry wires were showing 42.9 sme as the cell when under charge

 

[Tench]

Which makes me think you have the pack wired up wrong, it looks like that one cell has been wired between the ends of the pack in parallel to the other 11 instead of in series with them?

 

[StrapYourSelfIn]

the pack has been running for a 6 months and once a week I have been testing all the cells individually and in series. Just the other day it did this.

Could it be the cell just died?

 

[StrapYourSelfIn]

its 12 cells

(-) -|1|--|2|--|3|--|4|--|5|--|6|--|7|--|8|--|9|--|10|--|11|--|12|- (+)

cell 1 in the one thats dead (or so it appears)

i cant really get it in parallel as the one that is a problem is the first cell (-)

 

[StrapYourSelfIn]

(-) +|1|--|2|+-|3|+-|4|+-|5|+-|6|+-|7|+-|8|+-|9|+-|10|+-|11|+-|12|+ (+)

wouldnt even run from what i understand

 

[dnmun]

did you try to charge up that cell and see how fast it drains back? if you shorted the shunt transistor on that channel it would drain the cell down so check for the voltage across the shunt resistors on that channel to see if the mosfet is shorted.

 

[Tench]

I think your wrong, if you have 42v between those 2 wires they must come from either end of the pack, from cell 2- to cell 12+, that is the only place you should be able to measure that voltage so the cell should only be connected to one of those wires to add it to the series, with the total pack voltage then measuring from the other wire to the end of the added cell.

It looks to me like you had that cell connected between the main pack outputs? which has probably killed it!

 

[999zip999]

From now on please write cell voltage as
1. 3.38V
2. 3.45V
3. 0.38V

12. X.xxv
Pack voltage 40.2v
These makes for ez reading.
Follow Dnmum's advice for the bms. But does sound like you killed that cell, but before changing find out what happing with the bms.

 

[StrapYourSelfIn]

@ 999zip999 @dnmun
I was down setting up to test the BMS as you suggested and while the BMS was not connected i connected the battery and put it under load.

No Load 40.8v
with load 2#.#v it fluctuated in the mid 20´s

Measured the voltage with all 12 cells connected but measured from the neg. after the dodgey cell.(so 11 cells)
no load 36.7v
load 36.7v (the motor wasnt running as it was still connected with all 12 cells and that voltage was in the mid 20´s)

I then measured the single cell still with all 12 connected
no Load 4.00v
Load .37v

Under load whenever I measured the full battery the fluctuation made the multimeter difficult to read an exact voltage.
Under load whenever I measured the full battery minus the dud cell it was 36.7

i think I can safely say its a dud cell. What can be things that can cause the cell to behave in this manner (in terms of things i can check ) besides it just being a dud cell off of the shelf.

ps.
just went down again and removed the dud battery from the pack all together,connected it all up and the board ran. i noticed the dud cell has .046V now,so replacing it will be the only option.
i will check the BMS fully when i get the new cell. But the way it deteriorated I think it was just the cell becuase it was all perfectly balanced a week before when i checked.

 

[amberwolf]

If that cell has very high internal resistance, compared to the rest of the pack, then it could show a very high voltage across it as current flow thru the pack trying to charge the other cells would develop a much higher voltage across it, and it probably would not absorb much charge, and appear "shorted out" and give a very low voltage reading when the charger isnt' connected.


If the cell outside the pack still reads at near-zero volts, then the cell is probably failed. If it reads normally outside the pack then perhaps the connections at the ends of the cell are simply high-resistance, and causing the problem. Fixing that might fix the pack problem, if so--otherwise you'd likely need to replace the cell.

 

[StrapYourSelfIn]

@amberwolf you pretty much describe exactly whats happening. i have already contacted the supplier as they are only 6 months old. i also ordered 2 spares in case this occurs again.

Thanks for taking the time.

 

[999zip999]

Strap yourselfin where are you located ?

 

[dnmun]

not sure why you did not just test the BMS to see if that channel is shorted. none of the other stuff makes any sense and you learned nothing. there may be nothing wrong with the lifepo4 cell you removed, just drained down by the shorted mosfet.

 

[StrapYourSelfIn]

@dnmun way i see it,the battery is less than optimal. I can send it back and they will replace it. i will test the BMS when i get the other cell. i have a second BMS that I can replace the current one with if it is also faulty.
Considering the test was done with no BMS connected and the behavior of the battery stayed consistent with it being a failed cell i think .

I have moved the cell further up the pack and it behaved in the same manner